This invention provides a low cost means for achieving affordable solar energy by greatly reducing the cost of solar concentrators which increase (concentrate) the density of solar energy incident on the solar energy converter. A limiting factor in the utilization of solar energy is the high cost of energy converters such as photovoltaic cells. For example, for the purpose of generating electricity, a large area of expensive solar cells may be replaced by a small area of high-grade photovoltaic solar cells operating in conjunction with the inexpensive intelligent micro-optics of this invention. Thus the instant invention can contribute to the goal of achieving environmentally clean energy on a large enough scale to be competitive with conventional energy sources.
The rotatable elements of this invention are mirrored balls and cylinders. As derived in U.S. Pat. No. 6,612,705 of which one inventor of this instant invention is the co-inventor, balls in a square array have a packing fraction of 0.785 and 0.907 in a hexagonal array. Balls have an advantage over cylinders in that they can operate in either a single-axis or two-axis tracking mode. Cylinders have an advantage over balls in that they can have a packing fraction of nearly 1, but they are limited to a single-axis tracking mode. The elements 1 (balls and cylinders) may be individually oriented, or groups may be collectively aligned to simplify tracking and focussing. Different groups are given different orientations to achieve focusing. The number of mirrors per grid cell are a design variable. The voltages can be controlled by a small micro-processor (computer) with analog voltage outputs.
There is a trade-off between complexity of the grid, and size of the voltage source and control system. One element per grid cell is the maximum complexity of the grid and control system, and presents the minimal requirement for the voltage source. Unlike displays that require high resolution, groups of balls may be collectively oriented to simplify tracking and focussing. In the instant invention, separate groups or ensembles of mirrors are individually aligned, while the members of a group all receive approximately the same alignment. When groups are collectively oriented they may have a slight group concavity to aid in the focussing to the collector. The number of layers of balls (mirrors) varies from one layer to a few layers, so the size of the voltage source perpendicular to the layer or layers of balls need not be large. However alignment of large lateral groups of even one layer increases the size of the voltage source since the applied electric field is proportional to the voltage/grid spacing in the lateral direction. In order to affectively align 1 million elements (balls or cylinders) in a lateral layer in the manner of the prior art with a grid spacing 1000 times (10002=1,000,000) that of one element, a voltage 1000 times V would be needed. V is typically 50 to 150 volts for the alignment of one element, so that 50,000 volts to 150,000 volts would be needed for lateral control in the conventional manner. One object of the instant invention is to align large groups of balls with lateral voltages that are relatively small compared to 1000 volts.
The presence of rotatable mirrors in a solar concentrator presents either a dilemma or an opportunity with respect to the basic nature of the alignment implementation. Mirrors are normally made of a conductive metallic coating. In an applied electrostatic field, E, a dipole moment is induced in the metallic conducting material of the micro-mirrors because the charge distributes itself so as to produce a field free region inside the conductor. To internally cancel the applied field E, free electrons move to the end of each conducting mirror antiparallel to the direction of E, leaving positive charge at the end that is parallel to the direction of E. Another way to think of this in equilibrium is that a good conductor cannot long support a voltage difference across it without a current source. An induced electrostatic dipole in a pivoted conductor in an electrostatic field is somewhat analogous to an induced magnetic dipole in a pivoted ferromagnetic material in a magnetic field, which effect most people have experienced. When pivoted, a high aspect ratio (length to diameter ratio) ferromagnetic material rotates to align itself parallel to an external magnetic field.
If alignment is attempted in a conventional manner such as is used in Gyricon displays, the induced polarization electric dipole field in a mirror presents a dilemma since it is perpendicular to the zeta potential produced dipole field and the net vector is in neither direction. The “zeta potential,” is the net surface and volume charge that lies within the shear slipping surface resulting from the motion of a body through a liquid. The zeta potential is an electrical potential that exists across the interface of all solids and liquids. It is also known as the electrokinetic potential. The zeta potential produces an electric dipole field when a sphere is made from two dielectrically different hemispheres due to their interaction with the fluid surrounding it, with a pole adjacent to each hemisphere. One way to eliminate or greatly diminish the effect of the zeta potential is to make the surface of both hemispheres out of the same material. This would be quite difficult for Gyricon displays because they require optically different surfaces e.g. black and white, or e.g. cyan, magenta, and yellow for color mixing.
The 1998 Gyricon U.S. Pat. No. 5,717,515 of Sheridon, entitled “Canted Electric Fields for Addressing a Twisting Ball Display” is exclusively concerned with Displays. There appears to be no mention of any other application than Displays, either specifically or by general statement. In this Sheridon patent, no mention is made of a mirror in the gyricon balls, nor is there any mention of specular reflection as would be obtained from a mirror. On the contrary, means are discussed to increase diffuse reflection from the balls so the Gyricon display may easily be observed from all angles. Certainly there is no anticipation of a solar concentrator application, mirrored illumination and projection, solar propulsion assist, or any other micro-mirror application. Furthermore there is no mention of coupling means to the balls other than by means of the zeta potential dipole, or an electret dipole both of which are parallel to the Gyricon axis of symmetry which in the case of black and white balls goes through the vertex of the black hemisphere, the center of the sphere, and the vertex of the white hemisphere. Also there is no mention of an induced polarization electric dipole in the balls. An important distinction with respect to the instant invention, is that the Sheridon display patents are not concerned with alignment of large groups of balls. In fact the same alignment of the balls collectively in large groups would be antithetical to display patents since they require high resolution.
This Sheridon U.S. Pat. No. 5,717,515 focuses on different embodiments of “segmented electrodes” for Displays only, without mention of other applications. Nor does it assert that their invention may be applied more broadly. Yet, interestingly, some of the claims are quite general. Since claims should be a summary of the invention described in the specification, it appears that such broad claims are not warranted by the specification. These broad claims seem to conflict with the claims of the prior 1981 Goodrich U.S. Pat. No. 4,261,653, which is also quite specific, and also differs considerably from the instant invention.
The instant invention differs substantially from that of Sheridon and from that of Goodrich in the use of: mirrored balls and cylinders; induced polarization electric dipoles in the mirrors with or without permanent dipoles in electrets; the dipole fields being perpendicular to the axis of symmetry (rather than parallel); the alignment of large groups of balls by means of the use of orthogonally criss-crossed laddered electrodes with widely spaced rung electrodes to provide greater transparency of the active surface than in the Sheridon patent. Furthermore alignment is achieved with less power consumption, i.e. with smaller power supplies than would otherwise be necessary.
The instant invention is primarily concerned with method and apparatus for the group alignment of solar concentrator micro-mirrors. However, it has broader applications wherever mirrors are used for focussing such as for solar propulsion assist, illumination and projection of light, optical switching, etc.